Saturable core tuning inductor



Aug- 22, 1961 w. M. w. QUERFURTH 2,997,584

SATURABLE CORE TUNING INDUCTOR 2 Sheets-Sheet 1 Filed Feb. 19, 1958 N.SM

-WWE INVENTOR. Wi/he/m M W. Querfurh Aug 22, 1961 w. M. w. QUERFURTH2,997,584

SATURABLE CORE TUNING INnucToR Filed Feb. 19, 1958 2 Sheets-Sheet 2 u lIll" INVENTOR. Wilbe/m M. W. Querfurh BY W@ a xda Patented Aug. 22, i961i tice 2,997,534 SATURABLE CURE TUNING HNDUCTOR Wilhelm Max WolfgangQuerfurth, River Forest, Ill., as-

signor to Motorola, lne., Chicago, lll., a corporation of Illinois FiledFeb. i9, 1953, Ser. No. 716,108 6 Claims. (Cl. Z50-40) This inventionrelates generally to inductors, and more particularly to a saturablecore reactor of `an adjustable type which may be used to providetracking of a plurality of tunable electric circuits, such as those of aradio receiver.

Saturable core reactors have previously been used to provide control oftuned circuits in radio receivers and transmitters. Such units areadvantageous in that they may be remotely controlled and several tunablecircuits may be controlled in unison to vary their resonant frequencies.It is necessary, however, that some means of adjusting the saturablecore reactors be provided in order d to obtain and maintain a desiredfrequency relationship between the different tunable circuits. Saturablereactors presently used have been ditlicult to manufacture with theclose tolerances required and it has been difficult to adjust theincremental permeability thereof to provide the required frequencyrelationship.

The term incremental permeability when used herein means thepermeability of the core at a given increment of magnetizing force. Theterm initial permeability means the permeability of the core at Zeromagnetizing force. The term starting permeability means a particularincremental permeability at which the frequency of a tuned circuitincluding the reactor is at one of the limits of a desired bandwidth.

lt is an object of this invention to provide a simple and inexpensiveadjustable saturable core reactor.

Another object of the invention is to provide an improved saturable corefor a reactor, the initial and incremental permeability of which may bereadily adjusted.

A further object of the invention is to provide improved tunablecircuits haw'ng adjustable core inductors which may be readily adjustedto provide a desired frequency relationship so that they may then betuned in unison to provide tracking.

One feature of the invention is the provision of an 4 improved core fora saturable reactor including a pair of cup-shaped core elements eachhaving a rim and a central stud and which may be mounted face-to-face toform -a chamber having a central post around which an inductance coilmay be positioned. The core elements are provided with recessed portionswhich may be located either in the lrims of the cups 'or in the studs orin both, so that the cross-sectional tarea of the ilux path may bevaried by turning the core elements relative to each other, therebyfacilitating adjustment of the incremental permeability of the reactor.lf both the stud and the rim have slots, the initial permeability of thereactor may be kept substantially constant when the core elements areturned to adjust the incremental permeability. However, the reactor maybe provided with a slug in the stud to permit adjusting the initialpermeability of the reactor independently of the incrementalpermeability.

Another feature of the invention is the provision of a saturable corereactor `as described in the preceding paragraph mounted within a .spoolof insulating material around which a magnetizing coil may be wound sothat the inductance of the reactor may be varied by varying the currentin the magnetizing coil.

A further feature of the invention is the provision of an improvedsaturation tuning system for a radio receiver in which various tunablecircuits include saturable core reactors having turnable cup-shaped coreelements with slotted portions therein, so that a desired frequencyrelationship between the tunable circuits may be obtained by turning acore element to the proper setting.

Another feature of the invention is the provision of an improvedsaturable core reactor including a pair of cupshaped core elements eachhaving a rim and a central stud with recesses therein, and in which thecross-sectional area of the flux-path in the core is quite small so thatthe magnetizing force required to produce saturation is relativelysmall.

The invention is illustrated in the drawings in which:

FlG. l shows a part of the circuit of a radio receiver includingsaturable core reactors in accordance with the invention;

FIG. 2 is an enlarged cross-sectional view of an assem- `led saturablereactor having a cup-core whose incremental and initial permeability maybe adjusted by turning one of the cups;

FIG. 3 is a cross-sectional view of a cup-core similar to that shown inFIG. 2 but having an adjustable slug for controlling initialpermeability independently of incremental permeability;

FIG. 4 is a perspective view of the pair of cup-shaped core elementsshown in assembled relation in FlG. 2;

5 is a perspective view of the cup-shaped core elements shown inassembled relation in FIG. 3;

FlG. 6 is a plan view showing still another form of the cup-shaped coreelements;

FGS. 7, 8 and 9 are perspective views showing cupshaped core elements indifferent positions of adjustment; and

PEG. 10 is a graph showing various frequency characteristic curves of atuned circuit ihaving -an adjustable core saturable reactor associatedtherewith.

ri`he invention provides an improved adjustable satura able reactorwhich is especially suited for use in radio receivers and may provide,for instance, remotely controlled circuits for tuning a trunk-mountedautomobile radio receiver. The saturable reactor includes a pair of coreelements made of material having variable permeability and lowretentivity. The core elements are each formed in the shape of a cuphaving a rim and a central stud, and the pair is assembled with the rimsof the cups `and the ends of the studs in physical contact. A sleevemade of non-permeable material is placed around the central post formedby the stud portions, and a spool of nonpermeable material surrounds theoutside of the assembled core. A coil forming an inductance element iswound around the internal sleeve, and a magnetizing coil conductingenergizing current is wound `around the eX- ternal spool. Slots orrecesses are provided along the junction of the rim portions of the cupor at the junction of the stud portions or in both places. Accordingly,the `amount of contact `area between the core elements depends upontheir relative position, and by turning one of the core elements withrespect to the other, the amount of Contact area may be varied. Thecontact `area in turn controls the incremental permeability of theentire core assembly, and consequently it controls the inductance of thecoil and ultimately the frequency change characteristic for a tunedcircuit in which the inductance coil is used. This may be used in amultiple tuned circuit receiver to set the value of a `uned circuit sothat its frequency characteristic bears a desired relationship to thefrequency `characteristic of other tuned circuits. The resonantfrequency of a tuned circuit may be controlled by changing the level ofthe energizing current in the magnetizing winding, and when severalreactors are used in different tuned circuits, the desired frequencyrelationship between the circuits can be maintained when the level ofthe energizing current in the magnetizing winding is varied. The initialpermeability of the reactors may be controlled separately from theincremental permeability thereof to ensure that the desired frequencycharacteristics are obtained exactly.

ln FlG. 1 there is shown a part of the circuit for a radio receiveradapted to be installed in the trunk of an automobile and remotelycontrolled. The receiver circuit includes saturable core reactors 10, f1and f2 in accordance with the invention whichV provide the tuning systemfor the receiver. The antenna l5 picks up radio frequency signals whichare applied to the radio frequency amplifier stage 22 by the capacitor21. The frequency of the signals applied to the radio frequencyamplifier stage 2.2 is controlled by the tuning circuit 17, and thefrequency of the output of the radio amplifier stage 22 is controlled bylthe tuning circuit 39. The amplified signals are applied by thecapacitor 23 to the converter stage 24% where the signals areheterodyned and converted to an intermediate frequency. The frequency ofthe oscillator signal utilized in the heterodyning action is controlledby the tuned circuit llt. The heterodyned signals are then applied to anintermediate frequency amplifier stage 25, and the audio frequencycomponent of the signals is detected in a detector stage 26. The resuling audio frequency signal is then amplified in the stage 27 and appliedto a loudspeaker 28 which couvents the signal to sound energy. Anautomatic gain control voltage is developed at the detector stage 26 andis `applied by a line 29 and a resistor 3@ to the radio frequencyamplifier stage 22 ina well-known manner.

The resonant frequency of each of the tuned circuits i7, 18 and 19 iscontrolled by the saturable core reactor included therein. The tunedcircuit 17 for the antenna 15 includes a capacitor i6 and a coil 51coupled in parallel. The coil 3l forms a part of the saturable corereactor 10, and its inductance value may be varied by changing theamount of current in the magnetizing 'coil 52. This is accomplished bychanging the setting of the slider dit on the potentiometer 51, andsince the potentiometer 5i may be located at a remote position, thismethod of tuning is particularly well suited for use with trunk-mountedradio receivers where the receiver proper is carried in the trunk of avehicle land only the potentiometer need be mounted on the dashboard.

The tuned circuit i9 for the radio frequency amplifier stage 22 issimilar to the tuned circuit 17, with a capacitor 4l and an inductancecoil 32 being coupled in parallel. The coil 32 is provided by saturablereactor ll, the magnetiz-ing coil 54 of which is coupled to the slider64 of the potentiometer 5d by the radio frequency choke coil 53.

The tuned circuits i7 and i9 should be setto resonate at the samefrequenc and this frequency relationship `should be maintained toprovide tracking when the frequencies are changed by :adjusting thepotentiometer 5l.

The tuned circuit 18 `for the converter stage 24 includes a capacitor 42coupled in parallel with an inductance coil 33 which forms a part of thesaturable core reactor l2. The magnetizing winding 63 of the reactor l2is coupled to another potentiometer 6l through the slider 62. Thereactor 12 also includes a tertiary winding d3 connected to the cathodeof the converter stage 24. The sliders 62 and 64 are mechanicallyinterlocked so that as the slider 64 is moved the slider 62 movesproportionately causing the tuned circuit l to track with the othercircuits.

A saturable core reactor 10, which may be used to provide all of thereactors used in the tuning system of FIG. l, is shown in assembledrelation in FIG. 2. The reactor includes a spool 7l made ofnon-permeable material such as plastic and has an internal chamber 72therein. The spool is provided with a threaded plug 73 which may beremoved to provide access to the chamber '72. The magnetizing coil 52 iswound on the exterior of the spool, and the chamber 72 receives `thecup-shaped core members 74 `and 75 which may be secured together by abolt 76 or other suitable fastening means to form the core of thereactor. The core members 74 and 75 include tubular stud portions 77which form a central post around which the sleeve i4 of non-permeablematerial is mounted. The hollow interior 93 of the post receives thebolt 76. An inductance coil 311 forming an element of the tuned circuitll7 is wound around the sleeve 14. The peripheral rim portions 79 of thecore elements extend around the outside of the coil 3l. Thus, the coil31 is completely surrounded by permeable material both internally andexternally so that the core provides a continuous flux path around andthrough the coil. A plurality of slots or recesses 33 are provided alongthe junction of the rim portions and the stud portions so that the fluxpath in the core is limited to the abutting segments between the slots.

The incremental permeability `of the core may be adjusted to obtain adesired frequency change characteristic for the tuned circuit 17, byvarying the contact area between the abutting segments. This is done byloosening the bolt 7 o and turning one of the core elements 74 and 75with respect to the other until the proper setting is obtained. Therelative disposition of ythe slots with respect to each other may bepredetermined such that the initial permeability of the `core may bemaintained nearly constant when one cup is turned. This separate controlover initial permeability is facilitated by ihaving the magnetizing coil52 wound about the outside of the rims 79 so that the core presents twoparallel paths to the saturating flux `generated by the core. As may beseen in FIG. 2, the path through the rims has a lower reluctance thanthe path through the studs so that saturating flux is mainly restrictedto the rims. However, the path presented to the flux generated by theinductance coil 31 is a loop as previously mentioned. Thus, incrementalpermeability may be adjusted by varying the contact area between therims 79 while initial permeability is controlled separately by varyingthe stud portion of the loop path to compensate for the rim adjustment.

The 'core elements 74- and 75 of FIG. 2 are shown in perspective in FiG.4. These elements are made `of a material having a variable permeabilitywith low retentivity and coercive force such as compositions known asferrite. The magnetic field which builds up around the inductance co-il3l is largely confined to the flux path presented by the core members.As previously mentioned, recesses are provided in the rim pontion 79 andthe stud portions 77 so that only `the abutting segments Sti and 8l cancome into physical contact. When the segments 80 are aligned, thesegments 3i. are offset. Since saturating ux is concentrated in the rims79, most of these flux linkages are made through the rim segments 8i?.The maximum crosssectional area of this iiux path through the core isobtained when segments 80 are aligned with each other as shown in FIG.7. When one of the members 74 and 75 is turned relative to the other toa position such as that illustrated in FIG. 8, the area of contactbetween the abutting segments Sti is reduced whereas the contact areabe- `tween segments 8l increases. The reluctance of the liux paththrough the air gaps provided by the recesses in the rims is muchgreater than that through the segments 80, and therefore the flux in therim is largely restricted to this reduced contact area, therebyincreasing the ilux density therein. This means that the core is morenearly saturated and its permeability is reduced. The initialpermeability remains comparatively unaltered, however, because thisproperty is controlled to a greater extent by the contact area betweenthe stud segments 8l which increases to offset the decreasing contactarea between rim segments 80.

If the core elements are turned to lthe position illustrated in FIG. 9,the rim segments 80 are completely olfset from each other and the rimflux path is interrupted by a continuous air gap which minimizes themagnetizing force on 'the cup members and produces a much lower level ofcore saturation.

The inductance value of the `alternating current carrying coil 13ldecreases `as the incremental permeability of the core decreases. Itfollows, then, that the permeability of the core may be adjusted byturning the core elements relat-ive to one another to vary the area ofcontact between the abutting segments 80 until a desired inductancevalue for the coil has been obtained. This operation is known as settingthe starting permeability of the core. The magnetizing force required toestablish the starting permeability is Supplied by the current in themagnetizing coil. This biasing current may be a direct current or analternating current having a direct current component. Of course, thebiasing magnetizing force may be supplied by using a permanent magnetinstead of a coil, or a coil and a permanent magnet may be usedtogether. Once the starting permeability is set, the inductance of thecoil 31 is varied to change frequency by changing the current level inthe magnetizing coil such vas by adjusting the po tentiometers SI1 and61 of FIG. l. If an alternating current is used in the magetizing coilthere will be a modulation of frequency.

FIG. 5 shows another embodiment of the invention in which the members 74and 75 are similar to those shown in FIG. 3 except that the studportions 77 are not provided with a recess or slot. The slots areprovided only in the rim portions 79 so that only the abutting segments80 may be variously positioned to control the incremental permeabilityof the core. Projections 91 on the rims 79 are provided to helpconcentrate more of the saturating flux in the n'ms as opposed to thestud. FIG. 3 shows the cups 74 and 75 of FIG. 5 in assembled relation.The incremental permeability is adjusted by turning one cup relative tothe other. This embodiment particularly lends itself to the provision ofa control for adjusting initial permeability independently ofincremental permeability. This may be accomplished by turning thethreaded Slug 92 to move it in or out of the hollow interior of the postformed by studs 77. Only the cup 74 is threaded so that the slug mayextend into cup 75 without interfering with the turning movement of thecups. The slug 92 may be made of the same ferrite material used for thecups.

FIG. 6 shows still another embodiment of the invention in which a slot83 is provided in the stud portions 77 and not in the rim portion 79. Inthis embodiment, the rim portions 79 abut against each other along theentire circumference of the core elements, and this construction has theadvantage that the inductance coil 31 is more completely shielded insidethe core.

The feature of adjustability of the core of the invention provides ameans for obtaining desired frequency change characteristics fordifferent tuned circuits such as the tuned circuits 17, 1S and 19 shownin FIG. l. A family of curves representing various frequency changecharacteristics for the tuned circuit 17 of FIG. l is shown in FIG. 9.Curve A shows the change of resonant frequency of the tuned circuit 17in response to changing magnetizing current in the saturable reactor 10when the trim segments are adjusted to have maximum contact area as inFIG. 7. Curve B shows a plot of these same values when the rim segmentsare adjusted to have about onehalf of the maximum contact area as inFIG. 8, and curve C shows the plot when the rim segments have only aslight contact area.

Since the frequency change characteristics represented by the curves A,B and C vary with the incremental permeability of the reactor whichdepends on the setting of the core elements, it follows that the tunedcircuits 17 and 19 can be adjusted to have the same frequencycharacteristic by positioning the reactor core elements properly.Similarly, a desired frequency characteristic may be provided for thetuned circuit 18 by adjusting the capacitor 42 and the core elements ofthe reactor 12. These frequency characteristics are selected so that theproper relationship between the resonant frequencies of circuits 17, 18and 19 is maintained when the sliders'62 and 64 are moved. Since theinvention provides means for separately controlling the initialpermeability of the core, the

cores may be turned until the desired starting permeability is obtained,and the desired frequency characteristic will automatically follow. Iffurther minor adjustments of frequency are necesary, the capacitors 16,41 and 42 may be varied slightly. However, the necessity for suchcapacitive adjustments is minimized by the fact that the startingpermeability of the reactor can be adjusted comparatively exactly toprovide substantially the exact inductance values required for thedesired bandwidth.

While the above-described cup core elements have been shown as used inthe tuning circuits of a radio receiver, it is obvious that the coremembers and the inductance coil enclosed therein may be used as theinductor element of any circuit where it is desirable to have anadjustable inductor. The induotors are simple and may be inexpensivelyconstructed, and yet they are extremely effective in operation. Thereactors provide a very simple and convenient way of correcting andadjusting the frequency characteristics of a tuned circuit. At the sametime, they have a high Q value which is an important advantage in highfrequency applications. The cup-shaped construction of the core alsoprovides an effective shield to pro- -tect the inductance coil containedtherein from stray external elds. Since the flux linkages within thecore are confined to the rather narrow abutting segments, a variation inpermeability with a consequent change in the inductance of the coil maybe obtained with much less magnetizing force than would otherwise berequired. This means that the number of ampere-turns in a magnetizingcoil required to change the permeability is reduced.

I claim:

l. An adjustable saturable core reactor including in combination, aspool of insulating material having an enclosed inner chamber, saidspool having a removable plug portion for providing access to saidchamber, a pair of permeable cup members mounted in said chamber andeach having a rim portion and a central stud portion, said cup membersbeing joined rotatably with said stud portions and said rim portionscontacting each other, said cup members having a slot thereininterrupting at least one of the junctions therebetween so that the areaof mutual contact therebetween may be varied to adjust the incrementalpermeability of said core by rotating one of said members relative tothe other, means for controlling the initial permeability of said coreseparately from the incremental permeability thereof, means for lockingsaid cup members together, an insulating sleeve mounted over said studportions of said cup members, an inductance coil wound around saidinsulating sleeve, and a magnetizing coil wound around said spool forcontrolling the inductance value of said inductance coil by variablesaturation of said core.

2. A saturable core for use in an inductor including in combination, apair of variable permeability core members having a cup-like shape, eachof said members including a center stud portion aligned with andcon-tacting the center stud portion of the other of said cup members anda peripheral rim portion contacting the peripheral rim portion of theother of said members, said rim portions being recessed along a partthereof so that as one of said members is rotated relative to the otherthe crosssectional area of the flux path through said rim portions isvaried to adjust the incremental permeability of said core, and meansfor adjusting the initial permeability of said core separately from theincremental permeability thereof.

3. A saturable core for use in an inductor including in combination, apair of cup-like members made of variable permeability material eachhaving a circular rim portion and a central stud portion extendingaxially of said rim portion, said cup-like members being joined withsaid stud portions and said rim portions respectively engaging eachother to provide a magnetic ux loop-path, said rim portions havingprojecting segments and recessed segments between said projectingsegments with said projectving segments being in mutual contact witheach other, and

magnetic means movable axially of said stud portions for controlling theportion of said magnetic flux loop-path through said stud portions toprovide a desired initial permeability for said core, one of said cupmembers being rotatable relative to the other, with both said studportions and said rim portions respectively maintaining mutual contactthroughout a substantial range of rotation of said one cup member sothat as said one cup member rotates the mutual contact area of said rimportions varies to control the portion of said magnetic flux loop-paththrough said rim portions, thereby providing an adjustment forcontrolling the incremental permeability of said core.

4. A saturable core for use in an inductor including in combination, apair of variable permeability core members having -a cup-like shape,each of said members including a center stud portion aligned with andcontacting the center stud portion of the other of said cup members and`a peripheral rim portion contacting the peripheral rim portion of theother of said members, said rim portions having projecting segments inmutual contact and recessed segments adjacent said projecting segmentsso that as one of said members is rotated relative to the other thecross-sectional area of the flux path through said rim portions isvaried to adjust the incremental permeability oi said core, and saidstud portions having means to provide a desired initial permeability forsaid core.

5. A saturable core for use in an electrical inductor including incombination, a pair of core members each having a cup-like shape, saidcore members being formed of material the permeability of which Varieswith the magnetic field applied thereto, each of said members includinga center stud portion and -a circular peripheral rim portion, said coremembers being assembled together in axial alignment with said studportion of one member contacting the stud portion of the other memberand said rim portion of one member contacting the rim por- :tion of theother member, said rim portions each having a plurality of projectingsegments in mutual contact and recessed segments between said projectingsegments, so that as said core members are held in axial alignment andone of said members is rotated relative to the other the cross-sectionalarea of the linx path through said rim portions is varied to adjust thepermeability of said core, and said center stud portions of said coremembers being shaped so that said stud portions are in engagement forall rotational positions yor said core members and the common area ofcontact therebetween varies `with the relative rotational position ofsaid core members to provide a further control of the permeability ofsaid core.

6. in a tuning control for a radio receiver which includes at least twotunable resonant circuits which are tunable over different `ranges offrequencies that correspond to the tuning range of the radio receiver,and wherein said two resonant circuits must track each other throughoutsaid ranges of hequencies, the combination 8 therewith of inductordevices of the saturable type with one included in each of said resonantcircuits, and with at least one of said inductor devicesbeingmechanically adjustable to establish the required tracking relationbetween said resonant circuits, said mechanically adjustable inductordevice including -a saturable core including a pair of core members eachhaving a cup-like shape, said core members being formed of material thepermeability of which varies with the magnetic eld applied thereto, eachof said members including a center stud portion and a circularperipheral rim portion, means holding said core members assembled inaxial alignment with said stud portion of one member contacting the studportion of the other member and said rim portion of one membercontacting the rim portion of the other member, an inductance coilpositioned within said rim portions of said core members and about saidstud portions thereof, said rim portions each having a plurality ofprojecting segments in contact with each other and recessed segmentsbetween said projecting segments, so that as said core members are heldin axial alignment and one of said members is rotated relative to theother the cross-sectional area of the flux path through said rimportions is varied toV adjust the permeability of said core, and saidcenter stud portions of said core members being shaped so that said studportions are in engagement for all effective rotational positions ofsaid core members, and magnetizing coil means positionedcircumferentially about said rim portions of said members in position toprovide saturating llux in said core, said magnetizing coil means whenenergized for tuning providing varying uX in said members to vary thesaturation of said core and thereby vary the inductance value of saidinductance coil, said cup members being adjusted to a rotationalposition relative to each other wherein said stud portions and said rimportions form uX paths through the same which establish a desiredinitial inductance value of said inductance coil and a desired variationof the inductance value of` said inductance coil in response to theaction of said magnetizing coil means, and which flux paths furtherestablish a desired frequency change in the one of said resonantcircuits in which said mechanically adjustable inductor device isincluded in response to the action of said magnetizing coil means suchthat said one resonant circuit tracks with the other of said resonantcircuits.

References Cited in the tile of this patent UNITED STATES PATENTS FranceJuly 21, 1954

